There is a vacuum motor and distribution manifold in the trunk on the right side above the battery. The motor runs any time vacuum is required by the locking system. Next time, listen very closely. Your problem is unlikely to be vacuum motor or manifold related. It sounds like you just may have a gummed up latch assembly holding something in the wrong position. After many years the grease dries out and gets hard so the pieces don't move freely as they should. Unfortunately, you'll need to remove the door panel to find out. You can search this forum for step by step instructions.

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